1. Field of the Invention
This invention relates to a speaker and a diaphragm for use in speaker, and more particularly to a speaker of which peripheries of a diaphragm and a top-cover are supported by a frame and to the diaphragm for use in speaker.
2. Description of the Related Art
Heretofore, a dome speaker shown in FIGS. 2A and 2B is proposed as an example of above described speaker. FIG. 2A shows an exploded half-sectional view of the dome speaker. FIG. 2B shows a half-sectional view of the dome speaker.
As shown in FIGS. 2A and 2B, in the dome speaker, a magnetic circuit with a ring-shaped gap is composed of a disk-shaped pole-plate 10, a magnet 11 and a yoke 12. The magnetic gap 13 is a gap between a side surface of the pole-plate 10 and the yoke 12, with a substantially same interval throughout a circumference of the gap 13. Moreover, a frame 14 made of such as synthetic resin is formed integrally outside the yoke 12 composing the magnetic circuit. A frame assembly is composed of the frame 14 and the magnetic circuit.
Further, a diaphragm 15 with a substantially circle or oval shape in a plane view is disposed over the frame assembly. The diaphragm 15 includes a dome shaped vibrating portion 16, a concave portion 17 with a U-shaped section provided at an outer peripheral edge of the vibrating portion 16, an edge damper 18a provided at an outer peripheral edge of the concave portion 17, and an edge damper frame 18b provided at an outer peripheral edge of the 18a and having a surface in level to a radial direction of the 18a. The edge damper frame 18b is provided alongside a leveling surface 14b on top of the frame 14.
Moreover, the diaphragm 15 includes a rising portion 18c being provided at an outer peripheral edge of the edge damper frame 18b and rising substantially perpendicular to the outer peripheral edge integrally. The rising portion 18c is provided alongside an inner side surface 14a-1 of a convex portion 14a provided outside the leveling surface 14b of the frame 14. Furthermore, the diaphragm 15 includes a locking portion 18d being provided at a top of the rising portion 18c and having a surface in level to a radial direction of the diaphragm 15 outwardly. The locking portion 18d is provided to abut against an inner side surface 14a-2 of the convex portion 14a. 
Incidentally, an edge 18 is composed of the edge damper 18a, the edge damper frame 18b, the rising portion 18c and the locking portion 18d. Moreover, the diaphragm 15 is composed of the vibrating portion 16, the concave portion 17 and the edge 18 being formed integrally by such as hot press molding a sheet of synthetic resin film.
In such structure, when the rising portion 18c is located alongside the inner side surface 14a-1 of the convex portion 14a provided on the frame 14, centers of the diaphragm 15 and the frame assembly are aligned with no misalignment, so that the diaphragm 15 is to be attached to the frame assembly in the correct position. In other words, the rising portion 18c locates a position of the diaphragm 15 corresponding to the frame 14 in radial direction.
Further, when the edge damper frame 18b is located alongside the leveling surface 14b of the frame 14, the concave portion 17 is not located outside the magnetic gap 13, so that the diaphragm 15 is to be attached to the frame assembly in the correct position. In other words, the edge damper frame 18b locates a position of the diaphragm 15 corresponding to the frame 14 in perpendicular direction.
Therefore, the concave portion 17 can be located floatingly at a correct position in the magnetic gap 13 of the magnetic circuit. A voice coil 19 made of wound electrical wire is adhered to the concave portion 17. Therefore, the voice coil 19 and the concave portion 17 are located in the magnetic gap 13 of the magnetic circuit by the edge damper 18a to be supported resiliently. Moreover, with locking portion 18d abutting against the inner side surface 14a-2 of the convex portion 14a, the diaphragm 15 is supported more firmly.
Moreover, a frame-cover 20 for protecting the diaphragm 15 is provided over the diaphragm 15. An outer peripheral surface 20a of the frame-cover 20 is located nearer to the diaphragm 15 than an inner surface 20b. Further, a locking portion 20c, falling substantially perpendicular to the outer peripheral surface 20a integrally, is provided at an outer peripheral edge of the outer peripheral surface 20a. A part of the outer peripheral surface 20a of the frame-cover 20 is supported by a leveling surface 14a-3 provided at a top of the convex portion 14a. Further, the locking portion 20c abuts against an outer side surface 14a-4 of the convex portion 14a, so that the frame-cover 20 is supported more firmly.
Incidentally, in general, the larger a vibration area of the diaphragm 15 becomes, the more advantage a speaker has when playing with sufficient sound volume in low frequency band (base range). It is because the larger the vibration area of the diaphragm is, the heavier mass of the diaphragm becomes, so that the lowest resonance frequency (fo) can be set up lower. It is also because the larger the vibration area of the diaphragm becomes, the higher radiation impedance becomes and the higher sensitive sound pressures becomes.
However, in the dome speaker as described above, the leveling surface 14b for supporting the diaphragm 15 and the leveling-surface 14a-3 for supporting the frame-cover 20 are provided at different positions of the frame 14 respectively. Therefore, as shown in FIG. 2B, there is a problem that in a diameter of the whole speaker, a part S1 for supporting the diaphragm 15 and the frame-cover 20 becomes larger, a diameter S2, adding the edge damper 18a to the vibration portion 16 of the diaphragm 15 which actually vibrates, becomes smaller and resultingly the vibration area becomes smaller.
Further, in the conventional dome speaker as above described, the portion rising portion 18c stands up from the edge damper frame 18b toward the frame-cover 20. Therefore, for providing a inner side surface of the frame 14 alongside the outer side surface of the rising portion 18c, it is necessary to provide the convex portion 14a of the frame 14 outward from the outer side surface of the rising portion 18c in radial direction.
As shown in FIG. 2B, this also causes the problem that in the diameter of the whole speaker, the part S1 for supporting the diaphragm 15 and the frame-cover 20 becomes larger, the diameter S2, adding the edge damper 18a to the vibration portion 16 of the diaphragm 15 which actually vibrates, becomes smaller and resultingly the vibration area becomes smaller.